The present invention relates to an optical device comprising optical parts bonded together with an optically transparent adhesive material, an adhesive composition for forming the same and a bonding method.
Technologies for increasing communication capacity have been acquiring greater importance due to the spread of the Internet. Bonding technologies used for the assembly of optical parts and optical elements used in optical fiber communication systems require high reliability, accurate adjustment of refractive index (for connecting optical paths), precise position accuracy (for connecting lenses) and high heat resistance (solder heat resistance). For the assembly of optical parts, soldering, laser welding and an organic adhesive such as an acrylic resin or epoxy resin have been used, or adhesives composed of organic-inorganic composite materials prepared by a sol-gel method have been proposed. (i) Proceedings of the 48th ECTC, pp. 1178-1185, 1998 proposes a fluorinated or sulfur-containing epoxy adhesive and epoxy-acrylic adhesive and (ii) Journal of Non-crystalline Solids, vol. 80, pp. 557-563, 1986 or (iii) Intl. Congr, On Glass.S, pp. 429-436, 1986 discloses organic and inorganic adhesives prepared by a sol-gel method. (iv) Japanese Patent No. 1829914 discloses an optical element which is produced using a sol-gel adhesive composed of an alkoxide and a metal salt and (v) Japanese Patent No. 2786996 discloses a prism which is constructed using an adhesive composed of a sllicate and alkoxide. Further, (vi) U.S. Pat. No. 5,991,493 discloses an optical element which is fabricated using an organic-inorganic composite adhesive, for example, an adhesive obtained by hydrolyzing a sol consisting of polydimethylsiloxane, methyltriethoxysilane and phenyltrifluorosilane.
However, technologies and adhesives for bonding these optical parts involve the following problems.
As for soldering and laser welding methods, fixed position accuracy is unsatisfactory, or a laser light source or advanced technology is required. Epoxy adhesives and acrylic adhesives (i) are inferior in heat resistance of 250xc2x0 C. or more (solder heat resistance). Adhesives comprising an alkoxide and a metal salt (ii to vi) have such problems that the bonding strength of an adhesive layer is insufficient because a cohesive failure readily occurs in the adhesive layer and that bubbles remain by bonding together optical parts such as lenses, the adhesive layer becomes cloudy, or sufficient adhesion cannot be obtained because an alcohol formed by a hydrolytic reaction or water formed by a dehydration reaction is evaporated during thermal curing.
It is an object of the present invention to provide an adhesive composition which improves the above problems, has high adhesion strength and excellent heat resistance, and can be used to bond optical parts together without producing such a defect as cloudiness caused by bubbles by reducing the generation of bubbles at the time of curing.
It is another object of the present invention to provide a method of bonding optical parts using the adhesive composition of the present invention.
It is still another object of the present invention to provide an optical device comprising optical parts bonded together with the adhesive composition of the present invention.
Other objects and advantages of the present invention will become apparent from the following description.
According to the present invention, firstly, the above objects and advantages of the present invention are attained by an optical device comprising at least two optically transparent optical parts which are bonded together with an optically transparent adhesive layer, wherein the adhesive layer is formed from a matrix containing at least one type of specific atoms selected from the group consisting of silicon, titanium, zirconium, aluminum and germanium, and oxygen atoms, at least part of the specific atoms is bonded to other specific atom(s) through a polyvalent hydrocarbon group having 2 to 8 carbon atoms and directly bonded to at least one monovalent hydrocarbon group selected from the group consisting of an alkyl group, phenyl group, monovalent fluorine-containing hydrocarbon group and monovalent sulfur-containing hydrocarbon group, and the contents of the above specific atom, the polyvalent hydrocarbon group and the monovalent hydrocarbon group are adjusted such that the refractive index value of the adhesive layer approximates to the refractive index values of the at least two optically transparent optical parts.
According to the present invention, secondly, the above objects and advantages of the present invention are attained by an adhesive composition for bonding optical parts together, which comprises the following components (A), (B) and (C):
(A) organopolysiloxane having at least two alkenyl groups having 4 or less carbon atoms bonded to silicon atoms in the molecule;
(B) organohydrogenpolysiloxane having at least two hydrogen atoms bonded to silicone atoms in the molecule; and
(C) a platinum-based catalyst.
According to the present invention, thirdly, the above objects and advantages of the present invention are attained by a method of bonding optical parts together, which comprises placing an adhesive composition containing the above components (A), (B) and (C) between at least two optical parts to be bonded together and curing the adhesive composition.